Just to clarify, you would not be using the second ActionTek as a "router" in the valid configuration...it's only providing you with wired Ethernet (and wireless, if you choose) LAN connectivity in your home's local network on the second floor, using the Coax in the wall to extend the network up there. The primary ActionTek is your router and all devices would get their IP addresses and routing information from it...including the second ActionTek.
Thanks buckingham. I am getting a clearer picture with every post here.
I have an existing and free coax line on the second floor but no ethernet run. So I decided to purchase a $40 Actiontec from ebay as it will not only give me wired ethernet but also improve the wireless signal upstairs.